Turbochargers are widely used on internal combustion engines, and in the past have been particularly used with large diesel engines, especially for highway trucks and marine applications. In distinction to superchargers, which derive their power directly from the crankshaft of the engine, turbochargers are driven by the engine exhaust gases. Exhaust gases are directed to and drive a turbine, and the turbine shaft is connected to and drives the compressor. Ambient air is compressed by the compressor and fed into an intake manifold of the engine to provide the required boost. When a turbocharger is operated over a wide range of engine speed and load conditions, the turbocharger components may function outside the optimum design range and consequently suffer loss of efficiency that adversely affects engine performance and engine attributes like noise.
In the operation of a turbocharger employing a radial compressor, as airflow to the compressor increases, compressor efficiency decreases until air flow chokes with no further increase in flow rate possible. In contrast, as flow rate to the compressor decreases, flow separation occurs which may result in undesirable oscillation and noise generation by the air flowing through the compressor. All compressors have a low flow limit where they enter turbulent full flow reversal and experience surge. Compressor operation during choke and/or surge conditions is aerodynamically and mechanically undesirable for optimal compressor efficiency.
Other attempts to address surge and choke of the supply air to the compressor include the use of pre-whirl apparatus at the periphery of the compressor input opening. One example approach is shown in U.S. Pat. No. 3,922,108, where the pre-whirl apparatus includes a flow duct to the compressor with a rotary pivoted disc valve positioned within the flow duct to control the amount of air passing through the flow duct to a plurality of slanted vanes axially located around the flow duct at the compressor inlet. The slanted swirl vanes impart a swirl to the air directed from the flow duct through the slanted vanes into the compressor.
However, the inventors herein have recognized potential issues with such systems. As one example, the angle of the rotary pivoted disc needs to be varied in the abovementioned apparatus for proportional swirl control, requiring a complex control system. Additionally, the rotary pivoted disc, even when fully open, may itself be an obstruction to the air flow to the compressor can create turbulence and therefore noise. The air path obstruction also is likely to limit the maximum power potential of the engine.
In one example, the issues described above may be addressed by a system for a turbocharger, including a flow channel upstream of a compressor, forming an inner flow passage and an outer flow passage, a plurality of swirl vanes defining a downstream outlet of the outer flow passage, the downstream outlet fluidically connecting the outer flow passage to the compressor, and a recessable plate at an outlet portion of the inner flow passage, the outlet portion fluidically connecting the inner flow passage to the compressor.
In some examples, the system further includes a controller, wherein responsive to an intake air flow rate above a threshold, the controller includes instructions to position the recessable plate to fluidically connect the inner flow passage to the compressor, and responsive to the intake air flow rate below the threshold, the controller includes instructions to position the recessable plate to block fluidic connection of the inner flow passage to the compressor, diverting intake air flow entirely through the outer flow passage. Intake air exits the outer flow passage through the plurality of swirl vanes in a swirled pattern and flows to the compressor at a favorable incidence angle which reducing flow separation and therefore noise generation, increases compressor efficiency and therefore decreases compressor outlet air temperature.
In this way, flowing intake air to a compressor through a swirl device mitigates noise associated with compressor operation at low air flow rates, while preventing air flow obstructions during high air flow rates when the recessable plate is fully stowed. Thus, desired aircharge to the engine for meeting engine torque demands is provided, thereby enabling the compressor to function efficiently along a wide operating range, increasing overall efficiency of the turbocharger and the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.